The present invention relates to an improved patient support structure, and more particularly to a patient support structure having a plurality of gas-filled sacks upon which the patient is supported.
U.S. Pat. No. 4,488,322 to Hunt et al discloses a mattress and bed construction having inflatable air sacks mounted on the mattress and connected to ports of header chambers which are incorporated into the mattress. Air is supplied to the sacks via conduits connected to the header chambers. The mattress is laid on the rigid, tubular steel frame base of a standard hospital bed. The inflatable sacks are mounted transversely of the mattress and connected to the header chambers on opposite sides by releasable connectors. Air is passed into the header chamber on one side of the mattress and exhausted from the air sack on the opposite side through a corresponding exhaust header chamber. A control valve regulates the flow of air which is permitted to escape from the exhaust header chambers to permit individual control of the pressure and rate of flow of air through each air sack or group of air sacks. The air sacks are divided into groups so that the sacks in each group can be set at a pressure which is appropriate for the part of the patient's body which is supported at that point. The air inlet and exhaust ports and control valves are grouped together in a single housing or pair of housings located at one end of the mattress. The control valves prevent air leakage from one of the air sacks from affecting the remainder of the sacks. A bellows is provided for adjusting the contour or overall shape of the mattress, and remotely operated air valves are provided for operating the bellows. The remotely operated air valve comprises a chamber divided by a flexible diaphragm into an inlet and an outlet, the diaphragm being movable between two extreme positions. The outlet includes a tube which projects into the chamber, and at one of the extreme positions of the diaphragm, the end of this inlet tube is sealed by the diaphragm. When the diaphragm is at its other extreme position, the diaphragm allows air to escape into the chamber through the tube.
In U.S. Pat. No. 4,099,276 to Hunt et al, a support appliance is disclosed as having articulated sections in which at least one section is raised pneumatically by means of a bellows, the raisable section having a hinged connection with the adjacent section to allow relative movement of the pivoting sections longitudinally of the appliance during relative angular movement. A control valve is disposed between the bellows and a source of pressurized air, the control valve being arranged to feed air automatically to the bellows as required to maintain the bellows in a predetermined inflated condition. The valve is connected to the hinged portion of the bed by a mechanical connection such as a line and pulley system which is able to accommodate the movement of the hinged part relative to the fixed part of the bed because the axis about which the hinged portion pivots, is not fixed. This movable axis eliminates the problem of the inflated sacks preventing the desired pivoting movement.
U.S. Pat. No. 3,909,858 to Ducker discloses a bed comprising air sacks formed with excess material which is used to attach the sacks to an air supply manifold, with the air pressure cooperating with the excess material to create a seal.
British Patent specification 1,273,342, (inventor Hopkins), published on May 10, 1972, discloses an air fluidized bed having a plurality of inflatable air cells, which are either formed of porous material or provided with air escape holes that provide air circulation beneath the patient. As shown in FIGS. 3-5 of the British patent, the cells are contiguously arranged and disposed in three end to end or longitudinally aligned rows that are also transversely aligned, i.e., across the mattress from one side to the other. Valves are provided for independently inflating groups of cells so that the cells supporting the different regions of the patient can be provided with different levels of air pressure. The cells rest upon an articulatable bed frame. The supply of compressed air is temperature controlled and filtered. In an alternative embodiment, shown in FIG. 8, three cells are formed from a single piece of material, gussets or fillets being provided between the cells.
It is desirable for the custodial operator of a patient support structure to be able to transport a patient residing on the structure by transporting the structure instead of moving the patient to a separate transport device. This permits the operator to move patients to specialized treatment areas without the necessity of physically picking them up from the support unit and transferring them to a mobile unit. This is especially desirable with burn patients who cannot be moved without compromising their therapeutic progress. However, since most patient support structures with inflatable sacks rely on electric power supplied through a wall outlet for powering the device which keeps the sacks inflated, moving the structure requires some way of maintaining power, such as remaining connected to the wall outlet. This is because of the necessity of providing some means of making compressed gas available to the sacks of the patient support structure during the process of moving the patient support structure in order to maintain the gas flow and pressure at appropriate levels in the sacks.
In the past, solutions proposed to this problem have involved the provision of a battery powered electrical inverter which converts direct battery current into alternating current for use by an AC blower which forms part of the support structure and supplies gas to the sacks of same. Another proposal involves the provision of a separate battery/blower package which forms part of the gas distribution duct work of the patient support structure and takes over the gas supply function of the AC blower that requires a AC electric outlet.
Both of the proposed solutions are flawed on the grounds of both electrical efficiency and operator convenience. In both cases, one or more heavy, cumbersome devices must be attached to the patient support structure. The devices then limit the mobility of the entire patient support structure by increasing its length or width, and accordingly interfering with doorways and elevators during the transport process. Furthermore, the size and weight of the batteries which must be provided depend not only on the travel time anticipated by the transfer, but also upon the electrical efficiency of the process by which the battery power is converted into the compressed gas required by the sacks of the patient support structure.
Another problem with patient support structures having inflatable gas sacks is the sensitivity of the gas flow profile in the sacks to manufacturing and assembly tolerances in the valves which control the flow of gas supplied to the sacks. A further problem can be presented by the manner in which the gas is exhausted from the sacks, since the exhausting gas can be noisy and the temperature of the exhausting gas could be uncomfortable to the patient, if the exhaust occurs at a location where the patient might be affected.